Dispensing Apparatus

ABSTRACT

A pressurised metered dose inhaler ( 1 ) comprising: a reservoir ( 2 ) for containing pressurised product, a valve ( 9 ) having an inlet ( 11 ) communicating with the reservoir and an outlet ( 14 ) through which product is dispensed in use, a piece of magnetisable material ( 5 ), an armature ( 8 ) extending into proximity with the valve, and an electromagnet ( 7 ) surrounding at least a portion of the armature. Wherein the armature is coupled to, or forms part of, the valve such that controlled energisation of the electromagnet causes the armature to be either attracted to or repelled from the piece of magnetisable material one or more times to operate the valve for a controlled time period to effect dispensation of a metered dose of pressurised product from the reservoir through the valve outlet.

The present invention relates to a dispensing apparatus for dispensingmetered doses of pressurised products, typically for inhalation via theoral or nasal passages. In particular, the invention relates toprovision of a pressurised metered dose inhaler.

Pressurised metered dose inhalers are known for delivery controlleddoses of medicaments and other products. It is important to be able toaccurately control the volume of each metered dose of product dispensedby the pressurised metered dose inhaler. In a typical metered doseinhaler a metering valve is provided having therein a metering chamberwhich defines the volume of each metered dose to be dispensed. Controlof the volume of the metering chamber is critical to the accurateperformance of the metered dose inhaler. This can lead to highmanufacturing costs and the need for rigorous testing of components toensure that the necessary accuracy is achieved. In addition, it is knownthat such metering valves can be prone to variation in the volume of themetered doses dispensed during the lifetime of the valve. This can becaused by a number of factors including distortion, degradation andswelling of the components of the valve, particularly those involved inthe construction of the metering chamber. It is particularly the casethat the structure and stability of the seals used in such meteringvalves can affect the volume of the metered dose dispensed through thelifetime of the valve.

In order to attempt to overcome at least some of these problems, it isan object of the present invention to provide a dispensing apparatus inthe form of a pressurised metered dose inhaler which does not rely on anaccurately volumed metering chamber to control the volume of productdispensed on each actuation of the inhaler.

The present invention provides a pressurised metered dose inhalercomprising:

-   -   a reservoir for containing pressurised product,    -   a valve having an inlet communicating with the reservoir and an        outlet through which product is dispensed in use,    -   a piece of magnetisable material,    -   an armature extending into proximity with the valve, and    -   an electromagnet surrounding at least a portion of the armature,    -   wherein the armature is coupled to, or forms part of, the valve        such that controlled energisation of the electromagnet causes        the armature to be either attracted to or repelled from the        piece of magnetisable material one or more times to operate the        valve for a controlled time period to effect dispensation of a        metered dose of pressurised product from the reservoir through        the valve outlet.

Preferably, the piece of magnetisable material is in proximity to thevalve.

Attraction of the armature to the piece of magnetisable material mayopen the valve to effect dispensation of a metered dose of product fromthe reservoir through the valve outlet. Alternatively, repulsion of thearmature from the piece of magnetisable material may open the valve toeffect dispensation of a metered dose of product from the reservoirthrough the valve outlet.

Preferably, the valve comprises a valve stem axially movable within avalve body between open and closed positions, wherein with the valvestem in the open position dispensation of product through the valveoutlet is enabled, wherein the armature is coupled to, or forms part of,the valve stem. The valve stem may comprise one or more flanges andwherein the armature engages the valve stem by contact with the one ormore flanges.

Preferably, the armature is resilient and, in the absence of magneticforces, acts on the valve stem to bias the valve stem into a closedposition.

The valve may comprise an internal spring bias biasing the valve steminto the closed position.

Preferably, the valve stem comprises a transfer port communicating withthe valve outlet and wherein the valve comprises an outer seal sealingthe transfer port from the valve inlet when the valve stem is in theclosed position.

Movement of the valve stem into the open position may move the transferport past the outer seal into communication with the valve inlet toenable product dispensation through the valve via the transfer port andvalve outlet.

Preferably, the outer seal is formed from an elastomeric material.

The pressurised metered dose inhaler may further comprise a permanentmagnetic circuit comprising one or more permanent magnets.

In one embodiment, the piece of magnetisable material forms a singlepole piece extending from the one or more permanent magnets into closeproximity with the valve.

Preferably, movement of the armature into contact with the pole piece onenergisation of the electromagnet with a first polarity completes thepermanent magnetic circuit.

Preferably, the attractive permanent magnetic force between the polepiece and the armature when the pole piece and armature are in contactexceeds the resilience of the armature such that when the electromagnetis de-energised the pole piece and armature remain in contact.

Preferably, energisation of the electromagnet with a second, opposed,polarity causes the pole piece to repulse the armature such that thearmature breaks contact with the pole piece.

In another embodiment, the pressurised metered dose inhaler comprisestwo pieces of magnetisable material forming two pole pieces extendingfrom the one or more permanent magnets into close proximity with thevalve to define an air gap in which the armature extends.

Preferably, energisation of the electromagnet with a first polaritymoves the armature into contact with a first of the two pole pieces tocomplete the permanent magnetic circuit.

Preferably, the attractive permanent magnetic force between the firstpole piece and the armature when the first pole piece and armature arein contact exceeds the resilience of the armature such that when theelectromagnet is de-energised the first pole piece and armature remainin contact.

Preferably, energisation of the electromagnet with a second, opposed,polarity causes the armature to be attracted to a second of the two polepieces such that the armature breaks contact with the first pole piece.

Preferably, the controlled time period of operation of the valve isbetween 25 and 250 ms.

Preferably, the metered dose has a volume of between 5 and 300microlitres. More preferably, the metered dose has a volume of between10 and 100 microlitres.

The pressurised metered dose inhaler may further comprise a pressurisedproduct contained in the reservoir.

The pressurised product may be maintained at a pressure of between 15and 200 psig. Typically, the pressurised product is maintained at apressure of approximately 60 psig at a room temperature of approximately20 degrees Celsius.

The pressurised product typically comprises a volatile propellant. Thepropellant may comprise one or more of HFA134a, HFA227, with or withoutethanol being present at a level of between 1 and 30%.

Optionally the pressurised product contains a pharmacologically activeformulation.

The pressurised metered dose inhaler may further comprise electronicmeans for locking out operation of the valve for a predetermined timeperiod after each actuation of the valve.

The pressurised metered dose inhaler may further comprise an electronicdose counter.

The present invention also provides a method of dispensing a pressurisedproduct from a metered dose inhaler of the type comprising a valvehaving an inlet communicating with a reservoir in which the pressurisedproduct is contained and an outlet, comprising the steps of:

-   -   coupling an armature of an electromagnet to, or forming an        armature of an electromagnet as part of, a valve stem of the        valve,    -   moving the armature of the electromagnet by controlled        energisation of the electromagnet towards or away from a piece        of magnetisable material one or more times so as to move the        valve stem from a non-dispensing position to a dispensing        position for a controlled time period to effect dispensation of        a metered dose of pressurised product through the valve outlet.

Optionally, energisation of the electromagnet moves the valve into thedispensing position.

In one embodiment, on de-energisation of the electromagnet the armatureis moved away from the piece of magnetisable material by resilience ofthe armature so as to move the valve into the non-dispensing position.

In another embodiment, the metered dose inhaler further comprises atleast one permanent magnet arranged such that on de-energisation of theelectromagnet the armature remains in contact with the piece ofmagnetisable material until the electromagnet is re-energised with acurrent of opposing polarity.

Preferably, the controlled time period is between 25 and 250 ms.

Preferably, the volume of the metered dose is between 5 and 300microlitres.

The pressurised metered dose inhaler may be used with, for example, apulmonary, nasal, or sub-lingual delivery device. A preferred use of thepressurised metered dose inhaler is in a pharmaceutical metered doseaerosol inhaler device. The term pharmaceutical as used herein isintended to encompass any pharmaceutical, compound, composition,medicament, agent or product which can be delivered or administered to ahuman being or animal, for example pharmaceuticals, drugs, biologicaland medicinal products. Examples include antiallergics, analgesics,bronchodilators, antihistamines, therapeutic proteins and peptides,antitussives, anginal preparations, antibiotics, anti-inflammatorypreparations, hormones, or sulfonamides, such as, for example, avasoconstrictive amine, an enzyme, an alkaloid, or a steroid, includingcombinations of two or more thereof. In particular, examples includeisoproterenol [alpha-(isopropylaminomethyl) protocatechuyl alcohol],phenylephrine, phenylpropanolamine, glucagon, adrenochrome, trypsin,epinephrine, ephedrine, narcotine, codeine, atropine, heparin, morphine,dihydromorphinone, ergotamine, scopolamine, methapyrilene,cyanocobalamin, terbutaline, rimiterol, salbutamol, flunisolide,colchicine, pirbuterol, beclomethasone, orciprenaline, fentanyl, anddiamorphine, streptomycin, penicillin, procaine penicillin,tetracycline, chlorotetracycline and hydroxytetracycline,adrenocorticotropic hormone and adrenocortical hormones, such ascortisone, hydrocortisone, hydrocortisone acetate and prednisolone,insulin, cromolyn sodium, and mometasone, including combinations of twoor more thereof.

The pharmaceutical may be used as either the free base or as one or moresalts conventional in the art, such as, for example, acetate,benzenesulphonate, benzoate, bircarbonate, bitartrate, bromide, calciumedetate, camsylate, carbonate, chloride, citrate, dihydrochloride,edetate, edisylate, estolate, esylate, fumarate, fluceptate, gluconate,glutamate, glycollylarsanilate, hexylresorcinate, hydrobromide,hydrochloride, hydroxynaphthoate, iodide, isethionate, lactate,lactobionate, malate, maleate, mandelate, mesylate, methylbromide,methylnitrate, methylsulphate, mucate, napsylate, nitrate, pamoate,(embonate), pantothenate, phosphate, diphosphate, polygalacturonate,salicylate, stearate, subacetate, succinate, sulphate, tannate,tartrate, and triethiodide, including combinations of two or morethereof. Cationic salts may also be used, for example the alkali metals,e.g. Na and K, and ammonium salts and salts of amines known in the artto be pharmaceutically acceptable, for example glycine, ethylenediamine, choline, diethanolamine, triethanolamine, octadecylamine,diethylamine, triethylamine,1-amino-2-propanol-amino-2-(hydroxymethyl)propane-1,3-diol, and1-(3,4-dihydroxyphenyl)-2 isopropylaminoethanol.

The pharmaceutical will typically be one which is suitable forinhalation and may be provided in any suitable form for this purpose,for example as a solution or powder suspension in a solvent or carrierliquid, for example ethanol, or isopropyl alcohol. Typical propellantsare HFA134a, HFA227 and di-methyl ether.

The pharmaceutical may, for example, be one which is suitable for thetreatment of asthma. Examples include salbutamol, beclomethasone,salmeterol, fluticasone, formoterol, terbutaline, sodium chromoglycate,budesonide and flunisolide, and physiologically acceptable salts (forexample salbutamol sulphate, salmeterol xinafoate, fluticasonepropionate, beclomethasone dipropionate, and terbutaline sulphate),solvates and esters, including combinations of two or more thereof.Individual isomers such as, for example, R-salbutamol, may also be used.As will be appreciated, the pharmaceutical may comprise of one or moreactive ingredients, an example of which is flutiform, and may optionallybe provided together with a suitable carrier, for example a liquidcarrier. One or more surfactants may be included if desired.

The seals and gaskets of the valve of the pressurised metered doseinhaler may be formed from any suitable material having acceptableperformance characteristics. Preferred examples include nitrile, EPDMand other thermoplastic elastomers, butyl and neoprene.

Other rigid components of the valve, such as the valve body and valvestem may be formed, for example, from polyester, nylon, acetal orsimilar. Alternative materials for the rigid components of the valveinclude stainless steel, ceramics and glass.

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying drawings in which:

FIG. 1 is a schematic cross-sectional view through a first embodiment ofdispensing apparatus in accordance with the present invention in anon-dispensing position;

FIG. 2 is a schematic cross-sectional view of the dispensing apparatusof FIG. 1 in a dispensing position; and

FIG. 3 is a schematic cross-sectional view of a second embodiment ofdispensing apparatus in accordance with the present invention in anon-dispensing position.

As shown in FIGS. 1 and 2, the dispensing apparatus 1 in the form of apressurised metered dose inhaler comprises a reservoir 2 defining avolume 3 for holding a pressurised product in liquefied form. Typically,the product will comprise a suspension or solution of apharmacologically active formulation together with a volatile propellantsuch as HFA134a or HFA227 together with optional solvent such asethanol. The reservoir 2 is filled through an inlet closed by a plug 4.

A valve 9 is provided having an inlet 11 communicating with the volume 3of the reservoir 2. As shown in FIG. 1, the inlet 11 may comprise ahollow tube 13 spanning between volume 3 of the reservoir 2 and aninterior of a valve body 10 of the valve 9. The valve 9 furthercomprises a valve stem 12 which is axially moveable within the valvebody 10 from a non-dispensing, closed position as shown in FIG. 1 to adispensing, open position shown in FIG. 2. The valve stem 12 comprises afirst flange 17 located within the interior of valve body 10. A spring21 extends between an internal shoulder of the flange 17 and a shoulderof the valve body 10 to bias the valve stem 12 into the non-dispensingposition of FIG. 1. The valve stem further comprises second and thirdflanges 18 and 19 located exterior to the valve body 10, the use ofwhich will be described below.

A distal end of the valve stem 12 which protrudes from the interior ofthe valve body 10 comprises a hollow duct 22 terminating in an outlet14. A radial transfer port 20 is formed in the valve stem 12 providingcommunication between an exterior of the valve stem 12 and the hollowduct 22. A spray pattern block 15 may be located on the distal end ofthe valve stem 12 as shown in FIG. 1 to improve atomisation of productdispensed through the valve 9. The spray pattern block 15 may beprovided with turbulence generating formations 23 in order to maximiseturbulence of the dispensed product.

An outer end of the valve body 10 is closed and sealed by means of anelastomeric seal 16. The valve stem 12 forms a sliding interference fitwith an aperture formed at the centre of the outer seal 16.

As shown in FIG. 1, the valve 9 is located in a distal end 24 of a polepiece 5 formed from a piece of magnetisable material such as a ferrousmaterial such as mild steel or iron. The pole piece 5 is elongated andcontacts at an upper end a pair of bars 6 again formed from a ferrousmaterial such as iron or steel. An enlongate resiliently flexiblearmature 8 made from a magnetisable material such as spring steel issandwiched between the bars 6 and extends therefrom downwardly intoclose proximity with the distal end 24 of the pole piece 5 and the valve9. As shown in FIG. 1, a distal end of the armature 8 is provided withan aperture through which the valve stem 12 extends. As shown in FIG. 1,the armature 8 is coupled to the valve stem 12 at a position between thesecond and third flanges 18, 19 such that sideways movement of thedistal end of the armature 8 (as viewed in FIG. 1) in either directioncauses the valve stem 12 to move with the armature 8.

The dispensing apparatus further comprises an electro-magnet 7 in theform of a coil of electrically conductive wire which may be energised byan electric current using contacts and a power supply which are notshown in the schematic figures. An alternative means of providing theelectric current, (other than a battery), may be utilised, such ascurrent induced by the movement of the inhaler or its components.

In the non-dispensing position of FIG. 1, the transfer port 20 of thevalve stem 12 lies outside the valve body 10 sealed by the outer seal 16such that there is no path to atmosphere for pressurised productcontained in the reservoir volume 3. In order to dispense a dose ofpressurised product from the reservoir 2, the electro-magnetic coil 7 isenergised causing a magnetic field to be induced in the armature 8.Consequently, the distal end of the armature 8 is caused to be attractedto the distal end 24 of the pole piece 5. This movement of the armature8 causes the valve stem 12 to be moved inwardly relative to the valve 9into the position shown in FIG. 2 wherein the transfer port 20 of thevalve stem 12 is moved into the interior of the chamber body 10 past theouter seal 16. In this position, flow of pressurised product from thevolume 3 of the reservoir 2 may take place via the inlet tube 11, theinterior of the valve body 10, the transfer port 20 and the hollow duct22 of the valve stem. The product exits the outlet 14 of the valve stem12 and then passes through the pattern spray block 15 and is thendispensed to atmosphere. As will be clear, dispensation in this waycontinues until the valve stem 12 is moved back into position shown inFIG. 1. In the first embodiment shown in FIG. 1, de-energisation of theelectromagnet 7 causes a cessation of the magnetic field induced in thearmature 8. At this point, the natural resilience of the armature 8leads to the armature 8 tending to straighten thus moving the armature 8out of contact with the distal end 24 of the pole piece 5 and movementof the valve stem 12 back into the non-dispensing position shown inFIG. 1. This movement may optionally be aided by provision of theinternal spring 21 in the valve 9, although it will be appreciated thatthe spring 21 may be dispensed with and the armature 8 alone used tomove the valve stem 12 back into the non-dispensing position. Thearmature 8 is prevented from fully straightening by contact of the firstflange 17 of the valve stem 12 with the outer seal 16 of the valve 9. Bytiming the period for which the electromagnet 7 is energised, and theorifice size of the transfer port 20 and other orifices of the flowpath, the volume of product dispensed in a single dose may be accuratelycontrolled. Preferably the volume of each dose of product is between 10and 300 microlitres. More preferably the volume is between 25 and 100microlitres.

Accurate timing of the energisation of the electro-magnet 7 iscontrolled by a microprocessor and control software (not shown in theschematic figures) housed in the metered dose inhaler. Theinitialisation of a dispensing cycle may be commenced by operation of amanual trigger by the user or by using some other triggering event suchas inhalation of the user.

The pressure of the product in the reservoir 2 is preferably between 15and 200 psig and more preferably the pressure is approximately 60 psigat a room temperature of approximately 20 degrees Celsius.

The piece of magnetisable material to which the armature 8 is attractedneed not be elongated and in this embodiment need not extend intocontact with the bars 6. Instead a discrete piece or block ofmagnetisable material may be provided in close proximity to the valve 9.The piece of magnetisable material may form part of the valve 9.

FIG. 3 shows a second embodiment of dispensing apparatus according tothe present invention. Like reference numerals have been used toreference like components with the first embodiment. Compared to thefirst embodiment, the apparatus has been amended by the provision of apermanent magnet 30 between the pole piece 5 and the bar 6. In otherrespects the construction of the apparatus is the same. In thisembodiment when the electromagnet 7 is energised, the armature 8 isattracted into contact with the distal end 24 of the pole piece 5 as inthe first embodiment. However, contact between the armature 8 and thepole piece 5 closes a permanent magnetic circuit incorporating the polepiece 5 and the permanent magnet 30, bar 6 and armature 8. Thus, in thisembodiment when the electromagnet 7 is de-energised, the armature 8remains in contact with the distal end 24 of the pole piece 5 since theattractive force between the armature 8 and the pole piece 5 caused bythe permanent magnet 30 is greater than the force created by theresilience of the armature 8. Contact remains and hence dispensing ofpressurised product continues until the electromagnet 7 is re-energisedwith an opposing polarity causing the armature 8 to be induced with amagnetic field of opposed polarity which leads to disruption of theattractive force between the distal end 24 of the pole piece 5 and thearmature 8. Consequently, the armature 8 breaks contact with the polepiece 5 and moves back into the non-dispensing position shown in FIG. 3.

Thus, in this embodiment, two energisations of the electromagnet 7 arerequired to carry out the dispensation of a single metered dose. Thefirst energisation moves the valve stem 12 into the dispensing positionto commence dispensation and the second energisation overcomes theattractive force between the armature and the permanent magnetic circuitto move the armature 8 back into the non-dispensing position to stopdispensation. By correct timing of the first and second energisations ofthe electromagnet 7, the volume of the metered dose dispensed may beaccurately controlled.

The direction of valve operation of the first and second embodiments maybe reversed such that attraction of the armature 8 into contact with thepole piece 5 moves the valve stem 12 into a non-dispensing position andmovement of the armature 8 out of contact with the pole piece 5 movesthe valve stem 12 into a dispensing position.

For both the first and the second embodiments, the apparatus may beamended by the provision of a complimentary piece of magnetisablematerial forming a second pole piece (and optionally a second permanentmagnet) arranged to have a distal end opposing the distal end 24 of thefirst pole piece 5 such that the armature 8 and valve stem 22 lie in anair gap between the end faces of the pole pieces. With such anarrangement, by choosing the direction of the current flow in theelectromagnet 7, the armature 8 can be caused to be attracted to one orother of the pole pieces. Attraction to one pole piece can be used tomove the valve stem 12 into the dispensing position and attractiontowards the other pole piece can be used to move the valve stem 12 intothe non-dispensing position. This arrangement allows for opening andclosing of the valve 9 both to be achieved using magnetic attractiveforces which allows for a potentially higher speed of response and morecertain closing of the valve. In turn this can increase the accuracy ofthe metered dose dispensed.

1. A pressurised metered dose inhaler comprising: a reservoir forcontaining pressurised product, a valve having an inlet communicatingwith the reservoir and an outlet through which product is dispensed inuse, a piece of magnetisable material, an armature extending intoproximity with the valve, and an electromagnet surrounding at least aportion of the armature, wherein the armature is coupled to, or formspart of, the valve such that controlled energisation of theelectromagnet causes the armature to be either attracted to or repelledfrom the piece of magnetisable material one or more times to operate thevalve for a controlled time period to effect dispensation of a metereddose of pressurised product from the reservoir through the valve outlet.2. A pressurised metered dose inhaler as claimed in claim 1 wherein thepiece of magnetisable material is in proximity to the valve.
 3. Apressurised metered dose inhaler as claimed in claim 1 whereinattraction of the armature to the piece of magnetisable material opensthe valve to effect dispensation of a metered dose of product from thereservoir through the valve outlet.
 4. A pressurised metered doseinhaler as claimed in claim 1 wherein repulsion of the armature from thepiece of magnetisable material opens the valve to effect dispensation ofa metered dose of product from the reservoir through the valve outlet.5. A pressurised metered dose inhaler as claimed in claim 1 wherein thevalve comprises a valve stem axially movable within a valve body betweenopen and closed positions, wherein with the valve stem in the openposition dispensation of product through the valve outlet is enabled,wherein the armature is coupled to, or forms part of, the valve, stem.6. A pressurised metered dose inhaler as claimed in claim 5 wherein thevalve stem comprises one or more flanges and wherein the armatureengages the valve stem by contact with the one or more flanges.
 7. Apressurised metered dose inhaler as claimed in claim 5 wherein thearmature is resilient and, in the absence of magnetic forces, acts onthe valve stem to bias the valve stem into a closed position.
 8. Apressurised metered dose inhaler as claimed in claim 5 wherein the valvecomprises an internal spring bias biasing the valve stem into the closedposition.
 9. A pressurised metered dose inhaler as claimed in claim 5wherein the valve stem comprises a transfer port communicating with thevalve outlet and wherein the valve comprises an outer seal sealing thetransfer port from the valve inlet when the valve stem is in the closedposition.
 10. A pressurised metered dose inhaler as claimed in claim 9wherein movement of the valve stem into the open position moves thetransfer port past the outer seal into communication with the valveinlet to enable product dispensation through the valve via the transferport and valve outlet.
 11. A pressurised metered dose inhaler as claimedin claim 10 wherein the outer seal is formed from an elastomericmaterial.
 12. A pressurised metered dose inhaler as claimed in claim 1further comprising a permanent magnetic circuit comprising one or morepermanent magnets.
 13. A pressurised metered dose inhaler as claimed inclaim 12 wherein the piece of magnetisable material forms a single polepiece extending from the one or more permanent magnets into closeproximity with the valve.
 14. A pressurised metered dose inhaler asclaimed in claim 13 wherein movement of the armature into contact withthe pole piece on energisation of the electromagnet with a firstpolarity completes the permanent magnetic circuit.
 15. A pressurisedmetered dose inhaler as claimed in claim 14 wherein the attractivepermanent magnetic force between the pole piece and the armature whenthe pole piece and armature are in contact exceeds the resilience of thearmature such that when the electromagnet is de-energised the pole pieceand armature remain in contact.
 16. A pressurised metered dose inhaleras claimed in claim 15 wherein energisation of the electromagnet with asecond, opposed, polarity causes the pole piece to repulse the armaturesuch that the armature breaks contact with the pole piece.
 17. Apressurised metered dose inhaler as claimed in claim 12 comprising twopieces of magnetisable material forming two pole pieces extending fromthe one or more permanent magnets into close proximity with the valve todefine an air gap in which the armature extends.
 18. A pressurisedmetered dose inhaler as claimed in claim 17 wherein energisation of theelectromagnet with a first polarity moves the armature into contact witha first of the two pole pieces to complete the permanent magneticcircuit.
 19. A pressurised metered dose inhaler as claimed in claim 18wherein the attractive permanent magnetic force between the first polepiece and the armature when the first pole piece and armature are incontact exceeds the resilience of the armature such that when theelectromagnet is deenergised the first pole piece and armature remain incontact.
 20. A pressurised metered dose inhaler as claimed in claim 19wherein energisation of the electromagnet with a second, opposed,polarity causes the armature to be attracted to a second of the two polepieces such that the armature breaks contact with the first pole piece.21. A pressurised metered dose inhaler as claimed in claim 1 wherein thecontrolled time period of operation of the valve is between 25 and 250ms.
 22. A pressurised metered dose inhaler as claimed in claim 1 whereinthe metered dose has a volume of between 5 and 300 microlitres.
 23. Apressurised metered dose inhaler as claimed in claim 22 wherein themetered dose has a volume of between 10 and 100 microlitres.
 24. Apressurised metered dose inhaler as claimed in any preceding claim 1further comprising a pressurised product contained in the reservoir. 25.A pressurised metered dose inhaler as claimed in claim 24 wherein thepressurised product is maintained at a pressure of between 15 and 200psig.
 26. A pressurised metered dose inhaler as claimed in claim 25wherein the pressurised product is maintained at a pressure ofapproximately 60 psig at a room temperature of approximately 20 degreesCelsius.
 27. A pressurised metered dose inhaler as claimed in claim 24wherein the pressurised product comprises a volatile propellant.
 28. Apressurised metered dose inhaler as claimed in claim 27 wherein thepropellant comprises one or more of HFA134a, HFA227, with or withoutethanol being present at a level of between 1 and 30%.
 29. A pressurisedmetered dose inhaler as claimed in claim 24 wherein the pressurisedproduct contains a pharmacologically active formulation.
 30. Apressurised metered dose inhaler as claimed in claim 1 furthercomprising electronic means for locking out operation of the valve for apredetermined time period after each actuation of the valve.
 31. Apressurised metered dose inhaler as claimed in claim 1 furthercomprising an electronic dose counter.
 32. A method of dispensing apressurised product from a metered dose inhaler of the type comprising avalve having an inlet communicating with a reservoir in which thepressurised product is contained and an outlet, comprising the steps of:coupling an armature of an electromagnet to, or forming an armature ofan electromagnet as part of, a valve stem of the valve, moving thearmature of the electromagnet by controlled energisation of theelectromagnet towards or away from a piece of magnetisable material oneor more times so as to move the valve stem from a non-dispensingposition to a dispensing position for a controlled time period to effectdispensation of a metered dose of pressurised product through the valveoutlet.
 33. A method as claimed in claim 32 wherein energisation of theelectromagnet moves the valve into the dispensing position.
 34. A methodas claimed in claim 33 wherein on deenergisation of the electromagnetthe armature is moved away from the piece of magnetisable material byresilience of the armature so as to move the valve into thenon-dispensing position.
 35. A method as claimed in claim 33 wherein themetered dose inhaler further comprises at least one permanent magnetarranged such that on de-energisation of the electromagnet the armatureremains in contact with the piece of magnetisable material until theelectromagnet is reenergised with a current of opposing polarity.
 36. Amethod as claimed in claim 32 wherein the controlled time period isbetween 25 and 250 ms.
 37. A method as claimed in claim 32 wherein thevolume of the metered dose is between 5 and 300 microlitres.